Pure CSS3 Smooth Drop-Down Menu

This menu is created only in CSS3 which is inspired from this post on Forrst! This consists of a nested ul structure to create the second level of the menu which is initially hidden with it's opacity set to 0. When the link is hovered, the respective ul shows up and slides down. This is achieved by setting its opacity to 1 and changing it's top offset when it's hovered in conjuction with the CSS3 transitions to animate the process smoothly.